Today's elevators are reliable and safe people movers. Unexpected failures or incidental interruptions of operation are rare and they are often caused by external disturbance factors, such as e.g. power failures, dirty sensors, frequently also by damage inflicted by hard impacts on mechanical structures of the elevator, such as e.g. doors. Although elevators generally do not cause an immediate risk of injury to elevator passengers or other people within the range of the elevator in the event of an operational shutdown, it is self-evident that in all situations passengers trapped in an elevator car have to be rescued as quickly as possible. However, elevator safety regulations require that the actions needed to allow the elevator to recover from a shutdown situation should be carried out safely without causing a risk of injury, which is why these actions may only be performed by authorized maintenance personnel. Typical shutdown situations are e.g. events where an elevator stops between floors, the door of an elevator car or a hoistway door does not open/close, or the elevator car does not start moving.
Often the monitoring of elevator operation is arranged in a centralized manner such that, from a single remote monitoring station, the operational state of a plurality of elevators generally located in the neighborhood is maintained and/or monitored. In their simplest form, remote monitoring stations are monitoring stations that take care of the reception and transmission of elevator alarms, or in their more advanced form monitoring stations that also take care of elevator condition monitoring and elevator surveillance. In situations of operational shutdown of an elevator, an alarm is transmitted to the remote monitoring station either automatically as an alarm activated by the elevator control system and/or manually, e.g. as an emergency call entered by an elevator passenger from inside the elevator car. Upon being notified about the operational shutdown of the elevator, the monitoring staff calls approved maintenance personnel to the place of alarm in accordance with the alarm request. The duty of the authorized maintenance personnel is to rescue all passengers trapped in the elevator car safely out of the car and to restore the elevator to the normal state of operation. This is often implemented by moving the elevator car to the nearest floor level with one or more of the elevator safety circuits bypassed (shunted).
A problem with monitoring arranged via a remote monitoring station is that in operational shutdown situations it may take unreasonably long for the maintenance personnel to reach the place of alarm, depending e.g. on the availability of maintenance personnel and their location relative to the place of alarm, smoothness of traffic in the area at different times of the day and many other external circumstances. Also, regional problem situations, such as widespread power failures, even earthquakes, may cause congestion in the transmission of maintenance requests and thus result in elevator passengers remaining trapped and waiting in elevator cars even for several hours before getting out. Some of the passengers may experience anxiety and/or stress if they have to wait long to get out. There also occur catastrophes, e.g. fires and/or earthquakes, where trapped passengers are in mortal peril and therefore have to be rescued as quickly as possible out of the elevator car.
Another problem is that an interruption of elevator operation may be caused by a minor and/or incidental fault that results in an operational shutdown situation that only requires a very simple maintenance action for the elevator to recover, but nevertheless authorized maintenance personnel have to be called to the site to correct the fault, as stipulated by the safety regulations. This results in extra maintenance visits, costs and unnecessarily long interruptions in normal elevator operation.
Prior art is described in U.S. patent specification Pat. No. 6,364,066, which discloses a system for rescuing elevator passengers from an elevator car in the event of operational shutdown of an elevator. In the solution disclosed, a check is made to ensure that control actions ordered from a remote control system do not involve a risk to the passengers in the elevator car before execution of the control actions. The disclosed solution is based on the use of, inter alia, on/off-type sensors monitoring the status of elevator car doors.
A problem with the prior-art solution is that it does not provide for comprehensive observation of the situation prevailing in the whole operating area of the elevator, but instead only aims at ensuring the safety of elevator passengers in the elevator car before remote control actions are executed. Therefore, for example the situation prevailing in the elevator shaft is not taken into account. Moreover, the use of on/off-type sensors for observing the status of operational elements, such as the status of doors, can easily lead to fatal errors if the sensors are defective and produce incorrect information about the actual state of the operational elements.